Nikolai F. Bondar

SEARCH FOR LIGHT SUPERSYMMETRIC BARYONS

We have searched for the production and decay of light supersymmetric baryons produced in 800 GeV/c proton copper interactions in a charged hyperon beam experiment. We observe no evidence for the decays R{sup +}(uud{tilde g}){r_arrow} S{sup 0}(uds{tilde g}){pi}{sup +} and X{sup -}(ssd{tilde g}){r_arrow} S{sup 0}(uds{tilde g}){pi}{sup -} in the parent mass and lifetime ranges of 1700{endash}2500 MeV/c{sup 2} and 50{endash}500ps. Production upper limits for R{sup +} at x{sub F}=0.47, P{sub t}=1.4GeV/c{sup 2} and X{sup -} at x{sub F}=0.48, P{sub t}=0.65GeV/c{sup 2} of less than 10{sup -3} of all charged secondary particles produced are obtained for all but the highest masses and shortest lifetimes predicted. {copyright} {ital 1997} {ital The American Physical Society}

Nuclear Dependence of Charm Production

Using data taken by SELEX during the 1996–1997 fixed target run at Fermilab, we study the production of charmed hadrons on copper and carbon targets withxa0Σ−, p, π−, and π+ beams. Parametrizing the dependence of the inclusive production cross section on the atomic number A as Aα, we determine α forxa0D+, D0, Ds+, D+(2010), Λc+, and their respective anti-particles, as a function of their transverse momentum pt and scaled longitudinal momentumxa0xF. Within our statistics there is no dependence of α on xF for any charm species for the interval 0.1<xF<1.0. The average value of α for charm production by pion beams is αmeson=0.850±0.028. This is somewhat larger than the corresponding average αbaryon=0.755±0.016 for charm production by baryon beams (Σ−, p).

First Observation of the Cabibbo-suppressed Decays Xi+(c) ---> Sigma+ pi- pi+ and Xi+(c) ---> Sigma- pi+ pi+ and Measurement of their Branching Ratios

The authors report the first observation of two Cabibbo-suppressed decay modes, {Xi}{sub c}{sup +} {yields} {Sigma}{sup +}{pi}{sup -}{pi}{sup +} and {Xi}{sub c}{sup +} {yields} {Sigma}{sup -} {pi}{sup +}{pi}{sup +}. They observe 56 {+-} 13 over a background of 21, and 23 {+-} 7 over a background of 12 events, respectively, for the signals. The data were accumulated using the SELEX spectrometer during the 1996-1997 fixed target run at Fermilab, chiefly from a 600 GeV/c {Sigma}{sup -} beam. The branching ratios of the decays relative to the Cabibbo-favored {Xi}{sub c}{sup +} {yields} {Xi}{sup -}{pi}{sup +}{pi}{sup +} are measured to be B({Xi}{sub c}{sup +} {yields} {Sigma}{sup +}{pi}{sup -}{pi}{sup +})/B({xi}{sub c}{sup +} {yields} {Xi}{sup -} {pi}{sup +}{pi}{sup +}) = 0.50 {+-} 0.20, and B({Xi}{sub c}{sup +} {yields} {Sigma}{sup -}{pi}{sup +}{pi}{sup +})/B({Xi}{sub c}{sup +} {yields} {Xi}{sup -}{pi}{sup +}{pi}{sup +}) = 0.23 {+-} 0.11, respectively. They also report branching ratios for the same decay modes of the {Lambda}{sub c}{sup +} relative to {Lambda}{sub c}{sup +} {yields} pK{sup -}{pi}{sup +}.

Precision Measurements of the {Lambda}{sup +}{sub c} and D{sup 0} Lifetimes

We report new precision measurements of the lifetimes of the {Lambda}{sup +}{sub c} and D{sup 0} from SELEX, the charm hadroproduction experiment at Fermilab. Based upon 1630 {Lambda}{sup +}{sub c} and 10210 D{sup 0} decays we observe lifetimes of {tau}[{Lambda}{sup +}{sub c}]=198.1{+-} 7.0{+-}5.6 fs and {tau}[D{sup 0}]=407.9{+-}6.0{+-}4 .3 fs .

New upper limit for the branching ratio of the Omega ---> Xi - gamma radiative decay.

We have searched for the rare hyperon radiative decay Omega- to Xi- gamma, using the Fermilab Proton Center 375 GeV/c charged hyperon beam. Our measurement of the Omega- beam fraction at 13.6 m from production is (4.8 +_ 0.4)10**(-5). No signal was found and we determine a new upper limit of (4.6 x 10**-4) at 90% CL for the Omega- to Xi- gamma branching ratio.